The present invention relates to a particular flight design and arrangement which has been found best suited to overcome a problem of hang up of stringy, elongate or fibrous materials, e.g. municipal waste, rubber tubing, rope, plastic, vegetable material, etc. within a rotary dryer. Hang up of such materials upon the edges of flights not only leads to non-uniformity of the product, but in some cases, stringy portions of a charge composition may be held up long enough and at a temperature high enough to ignite the material or cause it to char within the dryer. Moreover, the collection of stringy particulate material on the flights gradually causes a build up and eventual blocking of the apparatus. These problems are greatly alleviated in the structures embodying the present invention.
For the most part, rotary dryers in the past have consisted of a cylindrical shell having a plurality of similarly geometrically configured flights disposed at uniform circumferential intervals about the inner periphery of the shell. The dryer is mounted on suitable rollers or trunnions for rotation, and frequently inclined slightly to the horizontal to urge the material downwardly by gravity from the feed end toward the discharge end as it is repeatedly lifted and cascaded from the flights to the bottom of the dryer or an adjacent flight. For simple dehumidifying, for example, the drying of agricultural products, hot air may be used as a medium for abstracting moisture from the particulate material. The drying gases may be propelled in a direction counter to the flow of the material being dried, or in parallel, cocurrent relation to the material being dried.
Numerous modifications to this basic design of a rotary dryer have been proposed in the past including various inserts through the central portion of the dryer shell. These have taken various forms including stationary members as well as rotary members. A typical example of the latter is shown in U.S. Pat. No. 3,798,789 to Thompson. An annular type dryer of the vacuum type is shown in U.S. Pat. No. 2,837,831. A device which has compound flighting and an inner member is shown in U.S. Pat. No. 1,641,108 to West. Still another device for filtering sand or fines is shown in U.S. Pat. No. 3,076,270 to Madsen. U.S. Pat. No. 3,813,794 to Jawor teaches a rotary dryer device for tobacco or like material including guides supported interiorly of the dryer for cascading the material according to a predetermined path. One type of dryer used for drying of beet pulp includes a rotary shell having peripheral flights mounted therein, and a core composed of a plurality of X-shaped members disposed therein providing a honeycomb effect, the X's being disposed to permit material to fall through from one of the honeycomb members to the next.
The present invention is distinguished from the foregoing prior art in that it provides a rotary-type dryer characterized by at least three distinct zones: a feeding zone including a plurality of peripherally disposed flights or blades following a helical pattern; a distributing zone including a plurality of radially inwardly projecting flights or blades of similar geometric configuration at uniform circumferential positions; and the third zone for drying which is characterized by a plurality of flight support members or blades radially inwardly projecting from and secured to the rotary shell and characterized in that the leading edges thereof facing upstream toward the material feed end slope inwardly and rearwardly. Each of the support members carries a plurality of generally longitudinally extending flight members extending from either side thereof. It has been found that this particular design minimizes the hang up of fibrous or stringy materials and the problems which are encountered in other rotary dryer structures are apparently substantially avoided.